Mobile phones, personal digital assistants (PDAs), electronic pads, media players, digital cameras, MP3 players, televisions, monitors, interior and exterior lights, and other electronic devices use SSL devices (e.g., white light LEDs) for illumination. However, true white light LEDs are not available because LEDs typically emit light at only one particular wavelength. For human eyes to perceive the color white, a mixture of wavelengths is needed.
One conventional technique for emulating white light with LEDs includes depositing a converter material (e.g., a phosphor) on an LED. For example, FIG. 1A shows a conventional SSL device 10 that includes a support 2, an LED 4 attached to the support 2, and a converter material 6 on the LED 4. The LED 4 can include one or more light emitting components. For example, as shown in FIG. 1B, the LED 4 can include a silicon substrate 12, an N-type gallium nitride (GaN) material 14, an indium gallium nitride (InGaN) material 16 (and/or GaN multiple quantum wells), and a P-type GaN material 18 on one another in series. The LED 4 can be a lateral-type device that includes a first contact 20 on the P-type GaN material 18 and a second contact 22 on the N-type GaN material 14 spaced laterally apart from the first contact 20. Referring to both FIGS. 1A and 1B, the LED 4 emits blue light that stimulates the converter material 6 to emit light at a desired frequency (e.g., yellow light). The combination of the emissions from the LED 4 and the converter material 6 appears white to human eyes if the wavelengths of the emissions are matched appropriately.
FIG. 2A is a cross-sectional view of a conventional multi-LED device having a support 52, a plurality of LEDs 4 attached to the support 52, and a converter material 56 over the support 52 and the LEDs 4. The multi-LED device 50 also has a single lens 58 over the LEDs 4. All of the LEDs 4 are commonly connected to a common anode and cathode such that all of the LEDs 4 operate together. FIG. 2B is a top plan view of a common pattern for the LEDs 4 in conventional multi-LED devices. For example, conventional multi-LED devices typically have a two-dimensional grid of identical LEDs in which adjacent LEDs are spaced apart from each other by a constant distance throughout the entire array.
One drawback of the conventional multi-LED device 50 with a uniform LED distribution is that the intensity of light is greater at the center of the array than at the edge of the device. Such a non-uniform intensity distribution reduces the quality for backlighting and other applications because it creates dark spots around the edge of the array. For example, the light output intensity is substantially less at the corners of the multi-LED device 50 than at the center. To reduce the non-uniformity of conventional multi-LED devices, several manufacturers provide a diffusion film that diffuses light at the center of the LED array. Such diffusion films accordingly reduce the intensity of the light at the center of LED array, but this is undesirable because it reduces the overall light output and efficiency of multi-LED devices.